Processes and setups to obtain containers from rough shapes are now well-known. These allow the user to obtain containers that are able to sustain high temperatures and relatively severe mechanical pressure without losing their shape during use. In such processes, the molding is performed by blowing or by stretch-blowing, from a pre-form made of thermoplastic material whose body is brought to a temperature at least equal to the softening temperature of the material, and this results in an intermediary container of larger size than the finished container yet to be obtained; this intermediary container is then heated to obtain a rough shape of heated, shrunk body, which is then molded to form the final container.
Such processes and installation are, for example, known as European patent EP 442 836 in the name of the applicant.
Despite the fact that this process was vastly superior to previous techniques, it became obvious that the containers obtained by this process had a tendency to lose their shape when filled with hot liquids, and this made the container unstable. Then, the bottom structure itself was reworked, and it was found that the containers that had a curved bottom with an inward convexity, in other words containers with a "champagne bottom" because of the shape of the bottom which resembles that of a champagne bottle, could resist satisfactorily to these conditions.
The various processes and setups were tested and resulted in this type of final container bottom shape. It was determined that the containers that possess the best thermal or mechanical properties during use are those obtained from a rough shape possessing at least a curved primer of inward convexity in the central area, at the bottom on the final container. It was even noted that in certain applications that the rough shape must have a bottom whose shape and measurement must correspond to those of the bottom of the final recipient.
Therefore, the French patent request No 95 01507 presents a process and a setup that obtains a particular champagne-bottomed container from a rough shape whose bottom possesses the shape and size of the bottom of the final container.
Contrarily to the intermediary container and to the final container that are both obtained in a mold, the rough shape is obtained in air, after highly heating the body of the container and thus having provoked a relaxing of the constraints conferred to the thermoplastic material during the transformation of the pre-shape into the intermediary container. The result is that the rough shape resembles a container whose body is vaguely deformed or bloated, but that nevertheless possesses a bottom zone with a shape and dimension predetermined by the process used, that is to say either the final shape of the bottom of the final container, or a primer of the central part of the final container.
But, because of the relative indetermination of the shape of the body of the rough shape, it happens relatively often that the symmetry axis of the bottom zone is offset and/or tilted in relation to the axis of the finishing mold at the moment when the rough shape is placed inside of it. Actually, the positioning of the rough shape in the finishing mold is performed in the known manner with the neck, which is the only part that undergoes no deformation during the different steps of the transformation from a pre-shape to the final container.
The result is that sometimes the bottom area of the rough shape is not correctly centered at the moment of contact with the curved shape of the bottom of the mold, which often causes the bottom of the rough shape to get stuck on the curved shape of the bottom mold in an offset and/or tilted position, causing the final container to be misshapen and unsatisfactory.